The present disclosure relates to semiconductor processing, and more particularly, to a post metal chemical-mechanical planarization (CMP) cleaning process which can be used in advanced interconnect technology.
Defect reduction is perhaps the most critical task in yield and reliability improvement for semiconductor manufacturing. For back-end of the line (BEOL) processes with copper (Cu) interconnects, the defects associated with the chemical-mechanical planarization (CMP) process are quite often the major yield detractor to such an extent that their reduction becomes the most pivotal step in the successful qualification and implementation of the technology.
Since CMP is the final and enabling process before one level of Cu interconnect is fully defined, not only can it generate defects during the process per se (e.g., scratches and polish residues), but it will also reveal defects generated from prior processing steps, such as post-RIE cleaning, liner deposition, and Cu plating. Therefore, not only must the post Cu CMP cleaning process clean up the defects generated by CMP, it must also be sufficiently compatible with prior processes to prevent exacerbating pre-existing defects incoming to CMP.
In principle, a robust post Cu CMP cleaning process removes the polish residues (PR), foreign materials (FM), abrasive particles, or any debris left on the wafer surface as a result of the polish. In addition, a post Cu CMP cleaning process passivates the Cu surface long and effectively enough to inhibit time-dependent Cu corrosion in form of hollow metal (HM) and Cu nodules or dendrites (DE). With the ever shrinking ground rule, new challenges emerge and new types of CMP-related defects are observed in advanced technology nodes such as 32 nm and beyond. Among these, circular ring defects (sometimes referred to as brush scrubbing scratches) are unique in that such defects are generated during the brush cleaning step with distinct concentric circle signatures that follow the path of particles in motion on roller brushes, as shown in FIG. 1.
Small alumina or silica residual abrasive particles in CMP slurries are about 50 nm to 100 nm in diameter and are even more difficult to remove than larger particles due to their higher surface charge to volume ratio. Furthermore, in fine pitch Cu interconnects, the electric potential becomes greater while the diffusion path becomes shorter, creating an environment that will expedite the formation of corrosion-related defects such as HM and DE.
Previous work on post Cu CMP cleaning process includes the optimization of contact kinetics during brush clean to enhance cleaning efficiency and to reduce brush scrubbing scratches. Regarding the clean chemical, the addition of inhibitors, surfactants, or chelating agents is common practice in the industry. Currently, most of the post Cu CMP cleaning chemicals for advanced technology nodes operate in the neutral to high pH regimes in order to achieve acceptable passivation of Cu and prevent corrosion-related defects.
In view of the above, a new post metal CMP cleaning process is needed that overcomes the challenges associated with CMP.